A plurality of diode-or connected positive three terminal voltage regulators can be connected to a load in order to provide reliability through redundancy. However, when a diode is connected between the load and the output of a positive three terminal voltage regulator, the voltage regulation provided by such a regulator deteriorates. These regulators always maintain 1.25 volts between their output terminal and their adjustment terminal. As the load increases, however, the voltage drop across the diode connected between the load and the positive three terminal voltage regulator increases. Consequently the voltage available to the load decreases as does the voltage across a monitoring voltage divider.
The resultant signal from the voltage divider indicates a drop in output voltage. This signal causes the positive three terminal voltage regulator to increase its output voltage and as the output voltage increases so does the voltage drop across the diode. Therefore, in order to maintain 1.25 volts between the output and adjustment terminals the voltage across the voltage divider resistor decreases further since the diode and voltage divider resistor are series connected across the output and adjustment terminals. This decrease in voltage across the voltage divider resistor causes the positive three terminal voltage regulator to increase its output voltage even further until ultimately the regulator is completely out of regulation.
The output circuit of the present invention overcomes the out-of-regulation condition resulting from diode-or connected positive three terminal voltage regulators. This output circuit provides a highly regulated output when positive three terminal voltage regulators are connected to each other in a diode-or arrangement.